In the log processing environment, there is often a requirement to sort a pile of logs and index those logs so that they can be fed on to a conveyor belt or the like to form a continuous end-to-end chain of logs.
Numerous devices have been tried in the prior art to unscramble or sort, index and feed logs or like elongated objects from a stack of such objects. In the log processing environment generally a stack of logs is placed in contact with an unscrambling or sorting mechanism. The unscrambling or sorting mechanism attempts to disentangle and cull logs from the stack of logs and transport them away from the stack or pile of logs. A feeding and indexing mechanism attempts to transfer the logs one at a time from the unscrambling or sorting mechanism to form a continuous stream of logs moving downstream away from the stack of logs on some conveyancing means such as a conveyor belt.
One type of unscrambing or sorting mechanism is taught by Stelter in U.S. Pat. No. 5,119,930 which issued on Jun. 9, 1992 for a device entitled Quadrant Log Feeder. A movable quadrant having a curved peripheral surface is rotated over a fixed quadrant to raise at least one log from the logs' holding location and to deposit the logs against a conventional type of notched-disc singulator. The notched-disk singulator acts to index the logs one-at-a-time onto a conveyor belt.
Another type of unscrambling or sorting mechanism is a so called "step sorter" which forms part of the combined sorter/indexer mechanism disclosed in Canadian Patent No. 1,277,682 which issued to Interlog AB Sweden for a "Device for Piece Meal Transversal Feed of Longish Objects, Preferably Wood Pieces". A further unscrambling or sorting mechanism forms part of the combined sorter/indexer mechanism disclosed in United Kingdom Patent No. 1,256,509 which issued to Wellman-Cranes Limited for "Improved Means for Unscrambling Elongated Articles". Both of these devices rely on oscillating or translating one set of steps relative to a second set of steps so as to transfer any logs held in one particular step up to the next higher step. In step sorters, if the first stage of the step sorter, that is, the stage which is in contact with a pile of logs, does not on any one cycle pick up a log, then a blank is introduced into the stream of logs moving up the stepped ladder. Because each set of steps moves as a single unit, there is no way to re-engage the first stage of the step sorter with the pile of logs so as to place a log into the blank in the stream of logs.
One type of feeding and indexing machine is illustrated in U.S. Pat. No. 4,911,283 which issued to Hollins on Mar. 27, 1990. An earlier version of this machine is the subject of U.S. Pat. No. 4,624,361 which issued to Hollins on Nov. 25, 1986. U.S. Pat. No. 3,330,401 which issued to Ahlstedt on Jul. 11, 1967 also illustrates a feeding and indexing machine operating on somewhat similar principles to the Hollins device.
The Hollins and Ahlstedt devices feed and index logs which have been sorted from a pile of logs and delivered to their indexing mechanisms as a transversely oriented stream of logs. Both Hollins and Ahlstedt rely on an arm, or transverse array of arms, pivoting about an upstream pivot so as to bring a contact face on the arm or arms against the downstream-most log waiting to be indexed from the feeder queue. The arm or arms pivot in a direction opposite to the direction of movement of the stream of logs. That is, while the stream of transversely oriented logs are moving down the feed queue in, for example, a counter-clockwise direction as viewed from the side of the device, the arm or arms pivot in a clockwise direction.
Hollins indicates that log feeders utilizing the principles set out in his two patents are limited in the range of log sizes that can be accommodated by any one particular log feeder. It has been found that because logs are not of uniform diameter and are often warped and twisted, that log feeders employing the Hollins principle do not consistently feed logs on every cycle of the lift arms. That is, employing lift arms pivoting about an upstream pivot point so as to force the feeder queue to move back upstream, thereby allowing the lifting portion of the lifting arm located downstream of the feeder queue to cull one log (the downstream-most log) from the feeder queue and raise it so that the log can roll clear of the log feeder, does not consistently operate to cull a single log from the feeder queue.
In a log mill environment, it is important to be able to reliably feed one log after another onto a conveyancing means such as a conveyor belt because empty spaces left on the conveyor belt mean that the mill processor waiting at the downstream end of the conveyor belt is not being fully utilized. Conveyor belts convey the logs resting on them at a uniform speed. Empty spaces on the conveyor belt caused by an inconsistently operating log feeder mean that the downstream mill processor is not working at full or design capacity.